Under this head I shall attempt to show what it is that gives the appearance of that hollow or vacant space in which all things move so freely; and in what manner light, shade and colors, mark or point out the distances of one object from another, and occasion an agreeable play upon the eye, called by the painters a fine keeping, and pleasing composition of light and shade. Herein my design is to consider this matter as a performance of nature without, or before the eye; I mean, as if the objects with their shades, etc. were in fact circumstanced as they appear, and as the unskilled in optics take them to be. And let it be remarked throughout this chapter, that the pleasure arising from composition, as in a fine landscape, etc. is chiefly owing to the dispositions and assemblages of light and shades, which are so ordered by the principles called opposition, breadth, and simplicity, as to produce a just and distinct perception of the objects before us.

Experience teaches us that the eye may be subdued and forced into forming and disposing of objects even quite contrary to what it would naturally see them, by the prejudgment of the mind from the better authority of feeling, or some other persuasive motive. But surely this extraordinary perversion of the sight would not have been suffered, did ft not tend to great and necessary purposes, in rectifying some deficiencies which it would otherwise be subject to, though we must own at the same time, that the mind itself may be so imposed upon as to make the eye see falsely as well as truly; for example, were it not for this control over the sight, it is well known, that we should not only see things double, but upside down, as they are painted upon the retina, and as each eye has a distinct sight. And then as to distances ; a fly upon a pane of glass is sometimes imagined a crow, or larger bird afar off, till some circumstance has rectified the mistake, and convinced us of its real size and place.

Hence I would infer, that the eye generally gives its assent to such space and distances as have been first measured by the feeling, or otherwise calculated in the mind: which measurements and calculations are equally, if not more, in the power of a blind man, as was fully experienced by that incomparable mathematician and wonder of his age, the late Professor Sanderson.

By pursuing this observation on the faculties of the mind, an idea may be formed of the means by which we attain to the perception or appearance of an immense space surrounding us; which cavity being subject to divisions and subdivisions in the mind, is afterwards fashioned by the limited power of the eye, first into a hemisphere, and then into the appearance of different distances, which are pictured to it by means of such dispositions of light and shade as shall next be described. And these I now desire may be looked upon, but as so many marks or types set upon these distances, and which are remembered and learned by degrees, and when learned, are recurred to upon all occasions.

If permitted then to consider light and shades as tjrpes of distinction, they become, as it were, our materials, of which prime tints are the principal; by these, I mean the fixed and permanent colors of each object, as the green of trees, etc. which serve the purposes of separating and relieving the several objects by the different strengths or shades of them being opposed to each other, figure 6, plate 23.

The other shades that have been before spoken of, serve and help to the like purposes when properly opposed; but as in nature they are continually fleeting and changing their appearances, either by our or their situations, they sometimes oppose and relieve, and sometimes not, as for instance ; I once observed the tower-part of a steeple so exactly the color of a light cloud behind it, that, at the distance I stood, there was not the least distinction to be made, so that the spire, of a lead color, seemed suspended in the air; but had a cloud of the like tint with the steeple, supplied the place of the white one, the tower would then have been relieved and distinct, when the spire would have been lost to the view.

Nor is it sufficient that objects are of different colors or shades, to show their distances from the eye, if one does not in part hide or lay over the other, as in figure 6, plate 23.

For as in figure 2, plate 24, the two equal balls, though one were black and the other white, placed on the separate walls, supposed distant from each other twenty or thirty feet, nevertheless, may seem both to rest upon one, if the tops of the walls are level with the eye; but when one ball hides part of the other, as in the same figure, we begin to apprehend they are upon different walls, which is determined by the perspective: hence you will see the reason, why the steeple of Bloomsburychurch, in coming from Hampstead, seems to stand upon Montague house, though it is several himdred yards distant from it.

Since then the opposition of one prime tint or shade to another, has so great a share in marking out the recessions, or distances in a prospect, by which the eye is led onward step by step, it becomes a principle of consequence enough to be further discussed, with regard to the management of it in compositions of nature as well as art. As to the management of it, when seen only from one point, the artist has the advantage over nature, because such fixed dispositions of shades as he has artfully put together, cannot be displaced by the alteration of light, for which reason, designs done in two prime tints only, will sufficiently represent all those recessions, and give a just keeping to the representation of a prospect, in a print; whereas, the oppositions in nature, depending, as has been before hinted, on accidental situations and uncertain incidents, do not always make such pleasing composition, and would therefore have been very often deficient, had nattire worked in two colors only; for which reason she has provided an infinite number of materials, not only by way of prevention, but to add lustre and beauty to her works.

By an infinite number of materials, I mean colors and shades of all kinds and degrees; some notion of which variety may be formed by supposing a piece of white silk by several dippings gradually dyed to a black; and carrying it, in like manner, through the prime tints of yellow, red, and blue; and then again, by making the like progress through all the mixtures that are to be made of these three original colors. So that when we survey this infinite and immense variety, it is no wonder that, let the light, or objects, be situated or changed how they will, oppositions seldom miss; nor that even every incident of shade should sometimes be so completely disposed as to admit of no farther beauty, as to composition ; and from whence the artist has by observation taken his principles of imitation, as in the following respect.

Those objects which are intended most to affect the eye, and come most forward to the view, must have large, strong, and smart oppositions, like the foreground in figure 1, plate 25, also figures 4 and 5, plate 24, and what are designed to be thrown further off, must be made still weaker and weaker, as expressed in figure 6, plate 23, which receding in order, make a kind of gradation of oppositions; to which, and all the other circumstances already described, both for recession, and beauty, nature has added what is known by the name of aerial perspective; being that interposition of air which throws a general soft retiring tint over the whole prospect; to be seen in excess at the rising of a fog. All which again receives still more distinctness, as well as a greater degree of variety, when the sun shines bright, and casts broad shadows of one object upon another; which gives the skilful designer such hints for showing broad and fine oppositions of shades, as give life and spirit to his performances.

Breadth of shade is a principle that assists in making distinction more conspicuous; thus figure 2, plate 26, is better distinguished by its breadth or quantity of shade, and \'iewed with more ease and pleasure at any distance, than figure 3, plate 26, which has many, and these but narrow shades, between the folds. And for one of the noblest instances of this, let Windsor Castle be viewed at the rising or setting of the sun.

Let breadth be introduced how it will, it always gives great repose to the eye; as on the contrary, when lights and shades in a composition are scattered about in little spots, the eye is constantly disturbed, and the mind is uneasy, especially if you are eager to understand every object in the composition, as it is painful to .the ear when any one is anxious to know what is said in company, where many are talking at the same time.

Simplicity, which I am last to speak of, in the disposition of a great variety, is best accomplished by following nature's constant rule, of dividing composition into three or five parts, or parcels, see Chapter IV, on Simplicity: the painters accordingly divide theirs into foregrotmd, middleground, and distance or background; which simple and distinct quantities mass together that variety which entertains the eye ; as the different parts of base, tenor, and treble, in a composition in music, entertain the ear.

Let these principles be reversed, or neglected, the light and shade will appear as disagreeable as figure 2, plate 25, whereas, were this to be a composition of lights and shades only, properly disposed, though ranged under no particular figures, it might still have the pleasing effect of a picture. And here, as it would be endless to enter upon the different effects of lights and shades on lucid and transparent bodies, we shall leave them to the reader's observation, and so conclude this chapter.